Organic Wastes Amended with Sorbents Reduce N2O Emissions from Sugarcane Cropping

Maren Westermann,Nicole Robinson,Monica Salazar Cajas,Jaye Hill,Richard Brackin,Matthew Redding,Susanne Schmidt,Taleta Bailey,Weijin Wang,Ryo Fujinuma,Chris Pratt,Scott Buckley,Jitka Kochanek,Stéphane Guillou,Joao Carlos Martins Freitas

doi:10.3390/environments8080078

Abstract

Nutrient-rich organic wastes and soil ameliorants can benefit crop performance and soil health but can also prevent crop nutrient sufficiency or increase greenhouse gas emissions. We hypothesised that nitrogen (N)-rich agricultural waste (poultry litter) amended with sorbents (bentonite clay or biochar) or compost (high C/N ratio) attenuates the concentration of inorganic nitrogen (N) in soil and reduces emissions of nitrous oxide (N2O). We tested this hypothesis with a field experiment conducted on a commercial sugarcane farm, using in vitro incubations. Treatments received 160 kg N ha−1, either from mineral fertiliser or poultry litter, with additional N (2–60 kg N ha−1) supplied by the sorbents and compost. Crop yield was similar in all N treatments, indicating N sufficiency, with the poultry litter + biochar treatment statistically matching the yield of the no-N control. Confirming our hypothesis, mineral N fertiliser resulted in the highest concentrations of soil inorganic N, followed by poultry litter and the amended poultry formulations. Reflecting the soil inorganic N concentrations, the average N2O emission factors ranked as per the following: mineral fertiliser 8.02% > poultry litter 6.77% > poultry litter + compost 6.75% > poultry litter + bentonite 5.5% > poultry litter + biochar 3.4%. All emission factors exceeded the IPCC Tier 1 default for managed soils (1%) and the Australian Government default for sugarcane soil (1.25%). Our findings reinforce concerns that current default emissions factors underestimate N2O emissions. The laboratory incubations broadly matched the field N2O emissions, indicating that in vitro testing is a cost-effective first step to guide the blending of organic wastes in a way that ensures N sufficiency for crops but minimises N losses. We conclude that suitable sorbent-waste formulations that attenuate N release will advance N efficiency and the circular nutrient economy.

Highlights

Sugarcane, a giant perennial C4 grass, is one of the fastest growing terrestrial plants and a major global commodity [1]
emission factors (EF) of 3.4 to 8.0 in our study mostly exceeded the average EF of 3.87 ± 1.16% calculated for sugarcane soils globally [6]
0.04% to 6.7% from sugarcane fields fertilised with mineral N and managed with green cane harvesting [7,10,11,50,51,52], but were below the EF of 21% from Australian acid sulphate soil [8]

Summary

Introduction

A giant perennial C4 grass, is one of the fastest growing terrestrial plants and a major global commodity [1]. A limitation to sustainable sugarcane production is its N footprint. Only 50% of N fertiliser is used by sugarcane crops, with as little as 10–30% in main producer countries [2]. Nitrogen losses from sugarcane soils occur via leaching and run-off [3,4], ammonia volatilisation [5] and nitrous oxide (N2 O). Emissions [6,7,8,9,10,11]. Nitrous oxide losses from agricultural soils are in the global spotlight, as they dominate the estimated 7.3 Tg N2 O-N of annual anthropogenic emissions [12].

Methods

Results

Conclusion